So-called “open” operations may prove stressful for a patient. Thus, practitioners are resorting more and more to so-called “minimally invasive” operations, during which medical instruments are inserted through the skin (percutaneously), or into a natural passage of the patient (vagina, rectum, auditory canal, etc.), or into an artificial passage connected to the body of the patient (cannula, artificial vein, trocar, etc.). To this end, practitioners are assisted by images of the organ or organs in question, the images being taken before or during the intervention.
In urology, in order to detect a possible prostate cancer, it is known to carry out a prostate biopsy. This involves taking tissue samples from the prostate itself, said samples subsequently being analyzed in a laboratory in order to detect the presence of possible cancer cells. To this end, the patient is laid on his side or on his back. In the case of a transrectal biopsy, a medical instrument comprising a needle holder holding a biopsy needle is inserted into the natural passage, namely the rectum. By using the medical instrument, the clinician pierces the wall of the colon to reach the prostate and thus take prostate tissue samples. For the sampling, a two-dimensional ultrasound scan of the prostate, taken during the intervention in the form of a stream of images, is typically used by the clinician in order to position the needle relative to the prostate. However, the use of a two-dimensional image to carry out three-dimensional positioning, the relatively indiscriminate nature of an ultrasound scan as well as the rather symmetrical shape of the prostate and its mobility often lead to a significant positioning error of the needle relative to the prostate, so that the samples cannot in fact be taken regularly or in a targeted fashion, depending on the approach.
In order to help the clinician take the tissue samples at the appropriate positions, there are numerous devices for guiding the medical instrument.
For example, guide devices comprising an articulated arm controlled in order to move the proximal end of the instrument are known. The position of the proximal end in the reference frame of the fixed base of the articulated arm can therefore always be determined. Knowing the position of the prostate in the reference frame, it is thus possible to know the position of the instrument relative to the prostate throughout the intervention.
However, such a guide device is particularly bulky.
Moreover, such a guide device only takes into account the movements of the instrument. However, the patient may also shift during the intervention, which leads to movement of the prostate. For example, the patient may not be under local anesthetic and/or he may not be restrained, so that he can shift to find a more comfortable position, or simply by reflex. Merely the muscle activity of the patient, such as his respiratory cycle, may also cause the prostate to move. Furthermore, the prostate is a soft organ, so that the pressure of the instrument, or even merely the contact of the needle, without its being inserted into the prostate, is sufficient to move said prostate. In addition, the bladder fills and enlarges during the intervention. It may therefore press on the prostate so as to move the latter. Hematomas, or liquid accumulations, caused or not caused by the intervention, may also occur and cause movement of the prostate.
Thus, even if the position of the instrument in the reference frame is correctly determined, the prostate may shift so that the clinician cannot reach the initially intended region with the needle.
Guide devices comprising one or more transmitters (or markers) fixed to the instrument and a receiver (or detector of the markers), which is arranged in the room in which the patient is, are also known. For example, the transmitters generate induced currents which the receiver can detect, which makes it possible to position the transmitters, and therefore the instrument, in the reference frame of the receiver. Knowing the position of the prostate in the reference frame of the receiver, it is thus possible to know the position of the instrument relative to the prostate during the intervention.
In the same way, however, such a guide device is bulky and takes into account only the movements of the instrument, and in no way the possible movements of the prostate: the position of the prostate relative to the instrument is in fact rapidly displaced, and therefore lost. In other cases, it is possible to add additional sensors on an anatomical volume targeted by an intervention, in order to resolve this problem, but this invasive solution is not applicable to an intervention on the prostate, which is a soft internal organ.
Recently, a new class of guide devices has appeared, allowing the clinician to carry out punctures in the prostate more precisely. Specifically, said guide devices comprise an ultrasound probe provided with means for three-dimensional image acquisition. Said probe is arranged in the guide device in such a way that a position of the probe relative to the instrument is known, or at least can always be determined. For example, the probe is fixed to the instrument.
The probe therefore continuously provides images of the natural passage, the surrounding tissue and the prostate during the movement of the instrument in the natural passage. These images are then processed in order to determine the position of the probe, and therefore of the instrument, with respect to the prostate. Since the images contain information about the movements of the prostate, the guiding of the instrument is more precise. Patent Application FR 2 920 961 describes such a guide device.
However, ultrasound probes acquiring images in three dimensions present the drawback of requiring several seconds for the acquisition of an image. Furthermore, since the three-dimensional images contain a large amount of information, the processing of said images consequently also takes a few seconds. It is therefore not possible to know the position of the probe relative to the prostate rapidly enough after the start of the acquisition of a new image, so that the positioning of the instrument relative to the prostate still remains too imprecise. In addition, this approach lengthens the duration of the intervention.
In order to overcome the aforementioned drawbacks, a third class of guide devices is known, combining localization of the instrument with the images taken by an ultrasound probe (two dimensions, three dimensions, etc.) and localization by a transmitter/receiver assembly.
The transmitter/receiver assembly makes it possible to rapidly provide an approximate position of the probe, and therefore of the instrument, relative to the prostate. This position is used to initialize the processing of the images provided by the probe, the processing of the images then making it possible to refine the position of the probe relative to the prostate.
Thus, the position of the probe, and therefore of the instrument, relative to the prostate is adjusted around an overall position determined rapidly by the transmitter/receiver system.
Such a guide device makes it possible to localize the probe, and therefore the instrument, very precisely relative to the prostate, but requires both a probe/image-processing system and a transmitter/receiver system. In addition, the receiver is often bulky. Furthermore, external perturbations such as magnetic interference may hamper the localization of the receivers.
It has therefore been envisioned to replace the transmitter/receiver system with a sensor carried by the ultrasound probe.
However, such devices prove unreliable, particularly in the event of large movements of the prostate between the capture of a reference image and of a subsequent monitoring image. This is because, with such devices, the processing of the images makes it possible to refine the position provided by the sensor only with local optimization methods. However, if the organ moves significantly because the patient shifts during the intervention, the position provided by the sensor may lie outside what is referred to as the “capture range” of the intended solution (i.e. the actual position of the probe relative to the prostate) and it then becomes impossible for a local optimization calculation to reach this solution. In this case, these devices then perform as poorly as the guide devices comprising only a single sensor, since they can provide extremely erroneous and possibly dangerous positions. Furthermore, it proves necessary to calibrate the guide device regularly in order to reset it to a position which is known relative to the prostate, which is time-consuming and onerous for the operator.